Dremel 4000 Speed Controller Test

Thread Starter

JDR04

Joined May 5, 2011
367
I think I posted this in the wrong section hence very few responded.. Hopefully this is the right section now.

I have the above speed controller and would like to test if it is functioning the way it should but don't know how to go about it. The Dremel without any doubt overheated in use. After switching it off and resting it for a while, it just would not switch on again. I have also checked the switch which is fine.

I have attached a few photos hoping it will help. Could somebody please tell me how to go about this. I have a decent Fluke meter. The voltage in is 240Vac (UK). The 2 screws are where the 240vac is input. Right hand screw is positive. I checked the diodes on the back of the board and they all seem to be OK. (About 0.7v)

I would really appreciate some ideas on this. Thanks a lot folks.........Take care, stay safe.
 

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MaxHeadRoom

Joined Jul 18, 2013
25,979
Did the motor overheat or the control?
Dremels typically use a Universal (series) motor, Have you tried running the motor direct, i.e. 240v directly into the motor terminals.?
 

MisterBill2

Joined Jan 23, 2018
13,127
Indeed the very first thing to check is the motor, the brushes, and the power cord. There may be a thermal fuse embedded in the field coil, and those are intended to fail open if they get too hot.
 

Thread Starter

JDR04

Joined May 5, 2011
367
Did the motor overheat or the control?
Dremels typically use a Universal (series) motor, Have you tried running the motor direct, i.e. 240v directly into the motor terminals.?
Definitely the motor overheated. My own fault, I ran it till I could hardly hold it. Dumb.
 

Thread Starter

JDR04

Joined May 5, 2011
367
Indeed the very first thing to check is the motor, the brushes, and the power cord. There may be a thermal fuse embedded in the field coil, and those are intended to fail open if they get too hot.
I checked the thermal fuse which is attached to one of the brush holders and continuity was achieved.
 

MisterBill2

Joined Jan 23, 2018
13,127
I am assuming that there are also field coils, and two wires that are the connections to the motor, and that the motor can be turned easily by hand. If they get way too hot something can melt and stop the motor from turning.

The first check is safe and simple, which is to measure the resistance across the motor. The resistance should have a definite value, neither zero nor open. .

Then, for running, if you have a DC power source , a power supply of some kind, 24 volts would be good, connect the motor to that, apply power, and the motor ought to run at some low speed.
 

MaxHeadRoom

Joined Jul 18, 2013
25,979
A positive indication is measure the current at max rpm off load.
It should be fairly low, and is printed on the label of the drill.
Mine is 1.5a.
 

Thread Starter

JDR04

Joined May 5, 2011
367
I am assuming that there are also field coils, and two wires that are the connections to the motor, and that the motor can be turned easily by hand. If they get way too hot something can melt and stop the motor from turning.

The first check is safe and simple, which is to measure the resistance across the motor. The resistance should have a definite value, neither zero nor open. .

Then, for running, if you have a DC power source , a power supply of some kind, 24 volts would be good, connect the motor to that, apply power, and the motor ought to run at some low speed.
The field coil has 2 connections for the brushes and 2 connections for the blue and black wires from the speed controller.
IF I connect say 24Vdc to0 the input of the speed controller itself, should'nt I get some sort of variation in voltage on the speed controller output???
 

MaxHeadRoom

Joined Jul 18, 2013
25,979
The speed controller is designed for AC supply, if testing with DC, you need to feed the pair that go from the speed control to the motor.
IOW, direct to the motor.
IMO, 24v will not be close to a definitive test.
 

MisterBill2

Joined Jan 23, 2018
13,127
24 volts to the speed controller will probably do nothing. 24 volts to the motor itself might make it run slowly. Some higher voltage could make it spin faster.
If the motor reads open circuit then there is no point in going any farther until that is corrected. . That might be a thermal fuse in a field winding, or a worn out brush. or a brush not connected for some reason. But if there is some continuity then a momentary connection of mains power can show if it runs or not. "Momentary" in this instance is not over one second.
 

MrSalts

Joined Apr 2, 2020
2,354
The problem I see is that a connection to the full voltage mains is terribly unforgiving if something goes a bit wronge
The problem I see is that it is a $60 tool that is broken, the worst that can happen is the OP can buy a new one if he really needs one. I have had a drummel tool for years and rarely found it to be the best too for a job. Most hours on my drummel tools are when I let kids use them when they are not ready for larger tools. I see very little risk in blowing this thing apart by plugging it into 120vAC.
 
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MisterBill2

Joined Jan 23, 2018
13,127
I have discovered that the very small abrasive cut-off disc can be an incredibly valuable tool in places that I never thought about using it.
Not my most used tool, but certainly a valuable one. My advice holds regardless of the price.
And the cost may be much more i some parts of the world.
 

MaxHeadRoom

Joined Jul 18, 2013
25,979
Definitely the motor overheated. My own fault, I ran it till I could hardly hold it. Dumb.
If you are lucky, the armature may not be cooked, on most other Universal motors, you can tell very quickly if the motor is toast (armature short), as you would see a bright circular arc around the commutator.
Unfortunately with the closed in Dremel, it is virtually impossible to view the Com. when running.
 
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